Rhys Millen Truck Backflip Tech: Millen Explains What Went Wrong and Why the Second Attempt Will be Successful

Remember Rhys Millen's brash attempt to back flip a truck? It was supposed to happen in Las Vegas on New Year's Eve 2007. But the New Zealand-born stunt driver, drifter, and all-around adrenaline junky suffered a hard landing last December during a practice session for the jump, fracturing a neck vertebra, breaking his back, and wrecking the truck in the process. The official event in Sin City never happened. But Millen and Red Bull have announced they'll be at it again on December 31, 2008, attempting to achieve maximum hoonage in what they hope is the world's first successful back flip of a four-wheeled vehicle.

More From Popular Mechanics

We sat down with Millen to discuss the physics of what happened the first time. He also gave us the scoop on how he plans to battle gravity once more at a secret location in the Nevada desert. Millions will see the event when it's broadcast live during Red Bull: New Year. No Limits on ESPN at 8:00 P.M. PACIFIC (11:00 P.M. EASTERN), on New Year's Eve. Here's how he plans to make that jump a sucess. Fingers crossed. —Basem Wasef

Anatomy of a Crash: What Went Wrong

Though many factors contributed to Millen's ill-fated attempt to back flip a truck, it boils down to two variables: time and distance.

Several months before Millen's horrific landing, he and his team began experimenting with a 1/10 scale remote control vehicle. More than two hundred practice jumps later, Millen decided the actual stunt would be executed using a CORR Pro Lite off-road truck. Figuring that the truck needed serious help attaining the rotational momentum required to complete a full back flip, Millen devised a hinged extension to the ramp which kicks the front tires into the air and releases before the rear tires pass. Following dry runs with the "kicker" device on the ground (he likens it to a "speed bump on steroids"), Millen was confident enough with the concept to pass it onto his team, who started building an 18 foot tall, 8,000 pound ramp. They also assembled several thousand cubic feet of energy absorbing cardboard boxes for good measure.

With the truck stripped of its bodywork, Rhys performed practice jumps while his team tweaked the angle of the kicker and the truck's spring and shock settings. The RC car experiments revealed a nasty tendency for longitudinal mid-air rotation, due to the engine and drivetrain's rotational inertia. Millen figured that adding bodywork would act like a chute, create drag and reduce the rate of rotation. He added 4 mph to his departure speed in hopes of counteracting the truck's anticipated roll rate when the bodywork was bolted on, but that slight increase in speed led to the stunt's undoing. Because the four foot-long kicker was covered in a shorter period of time on his slightly faster run, the suspension didn't could not fully compress, rebound, and then hurl the truck towards its intended path. The sixteenth practice run ended with the truck overshooting the cardboard boxes and landing upside down.

During his physical rehabilitation following the crash, Millen swore he would take another stab at flipping a truck. He's been spending the weeks leading up to the second attempt practicing at Red Bull's training facility in Lake Piru, California where he'll perform trial runs using the world's largest foam pit.

Here's Five ways Millen and his team plan to make the jump successful:

A Longer Kicker: During the failed attempt, the 4 foot-long kicker didn't allow the suspension to rebound (due to the truck's faster speed), so Millen's next attempt will incorporate a longer, 5.5 foot kicker. "We will cover the kicker in .125 seconds," explains Millen, "so all of this will happen pretty fast." If it goes as planned, the truck's suspension will compress and rebound as it passes over the longer kicker, allowing it to execute a perfect back flip and land on all fours.

Slower Speed: "The 4-5 mph faster approach speed brought us to disaster," Millen says. That slight increase in velocity produced enough of a discrepancy in the truck's trajectory to send it crashing. Next time, Millen plans to launch at exactly 34 mph, which when coupled with the longer kicker and revised truck dynamics, will hopefully lead to a new world record and no more hospital bills.

Lighter Powertrain: In contrast to the 350 hp V8 that powered his first truck, Millen's second attempt will use a 2.4 liter 4-cylinder that produces 295 hp. Not only is it 200 lbs lighter (bringing the truck's total weight to a Miata-like 2,600 pounds), it will also make the truck's speed easier to modulate. "In testing we established that a constant approach speed and a lifting of the throttle at the point of striking the kicker reduced chassis roll during the rotation," Millen explains, "establishing that we no longer need an aggressive engine package."

Mass Centralization: The new engine has been moved closer to the center of the truck. The enhanced mass centralization will make it easier to control the truck's rotation.

Aerodynamics: One of the factors that resulted in the misjudgment of speed was the anticipation of how much drag bodywork would create on the truck. The truck's body will be identical the second time around, but now that the team knows how aerodynamics interplay with kicker length, departure speed, suspension settings, and other factors, it will become one less variable to worry about.

The Bottom Line

Millen and team Red Bull are leaving nothing to chance with their second attempt, having dissected what went wrong during the first go. "We didn't know the elements we'd be up against during the first jump," he admits, "and with the speed change and everything there were a lot of catches… unfortunately it didn't come out right," he says with a good natured laugh. "I guess that's why they call it an experiment."